array modifier overlapping
First select your object, the view that you prefer (in my case I'm using orthographic view). Then enter edit mode.



Now, you have a plane at the bottom, so to get a better view, let's hide that plane. To do so, rotate the view like the image. Please make sure you are in face selection, look at the top left of the image.



With the bottom plane selected, press H to hide the selection and then it will look like this.



Now go to top view => (numpad 7) and please make sure you are in orthographic view => (numpad 5)



Change to vertex selection on the top left corner



Change Wireframe (top right corner of image)



Now let's get to work:

First, select the vertex like in the image.



Then press S then Y then 0 (zero) and ENTER. What this means is that you are telling blender to "S" = scale all the selected vertices in the "Y" axis to 0, this will cause to all selected vertices to align in that axis.



Press Alt + A if you are in Blender 2.8 or just A if you are in a previous version to deselect the vertices. Then select the left side vertices like this.



Now repeat the alignment procedure but in the X axis, press S then X then 0 then ENTER.



Let's repeat the procedure on the right side.
First deselect all the vertices with (Alt A or A) depending on Blender version.
Now select the vertices like in the image.



Again S then X then 0 then ENTER.



Finally do the same on the bottom. Select the vertices (Don't forget to deselect the side vertices first).



Align the vertices on the Y axis (S then Y then 0 then ENTER).



Let's take a look at your object. Press Z and select solid.



Look that there are some discrepancies. There is a tiny gap and lack of roundness. Let's fix this.



Select the four vertices like in the image, now press "S" => scale then "X" for the x axis, hold down Shift and slowly move the mouse cursor to the center of the object to get the vertices closer to each other in the selected axis. Do this until you like the results.

Now for the gap, let's select the top and bottom vertices like in the image.



Press S then Y then hold shift and slowly move the mouse until the gap is closed.

Here is the result.



Hope this can help you. If you have any doubts let me know.